high side dc switching

Discussion in 'The Projects Forum' started by darryl, May 9, 2009.

  1. darryl

    Thread Starter Member

    May 1, 2009
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    Yeah, G`day. Could someone please show me by way of a diagram and circuit values a simple but effective way, either p-channel or n-channel, to shift 12v 5a thru the high side into a capacative load at a relatively low frequency. I have been trying to use 100v mosfets. Is the low voltage a problem?. Any assistance would be really appreciated. Thanks.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Not sure of what you need , but this should charge the cap in a hurry on a one time basis, or untill C is dumped.
     
  3. darryl

    Thread Starter Member

    May 1, 2009
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    Thanks Bernard. It`s working now. I was on the right track but had some values wrong. So, if I wanted to increase Vdd to 24v, does that mean I change the 2.2k to 4.7k and leave everything else the same?
     
  4. Bernard

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    2.2k ok, but need to be carefull not to exceed max. V S-G rating. Attachment might work, but needs peer review. Zener diode 12V.
     
  5. darryl

    Thread Starter Member

    May 1, 2009
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    Thanks Bernard. This is great stuff. I owe you. You have not included any resistance tied to the capacative load. Should I have at least some on there or is this not particularly mandatory?
     
  6. Bernard

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    I thought you had a load in mind, as it stands, it's only goal in life is to keep C charged up as long as it is fed clock pulses.
     
  7. darryl

    Thread Starter Member

    May 1, 2009
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    G`day Bernard. Ok, I understand about the load. One thing confuses me. You said a 2.2k would be ok for 24 volts but in your second circuit you have 22k. Would you mind clearing that up?
    Regards
    Darryl
     
  8. Bernard

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    Stick with 2*2k,or 2k2,or 2.2k. Now I see why some use *,or other means to boost visibility of .
     
  9. darryl

    Thread Starter Member

    May 1, 2009
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    Thanks Bernard. I have a question about solenoid construction. Can I ask you that or should I post a new thread. Regards. Darryl
     
  10. Bernard

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    You'll get more inf. on a post, and may help someone else.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    This is similar to Bernard's 2nd schematic, but I chose to use a 10v Zener to limit the maximum Vgs.

    If the Zener fails shorted, the MOSFET will never turn on. The specified Zener is rated for 1W, and in this configuration will be dissipating about 0.6W when the MOSFET is turned on.

    If R1 were decreased to around 500 Ohms (1/2 Watt), the turn-off time of the MOSFET would be improved, along with less load on the Zener (0.4W).
    [​IMG]
     
  12. darryl

    Thread Starter Member

    May 1, 2009
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    Hello Bernard. I just have a question about that 24v circuit. It would appear you have added a zener on the gate and a 10k resistor in series with the 2*2k. Could you please tell me about this resistor and how you arrived at that value. Regards. Darryl
     
  13. darryl

    Thread Starter Member

    May 1, 2009
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    If this message appears in triplicate, it`s not my fault. Could you please explain why you chose 10k for the resistor in series with the 2*2k in the 24v circuit. Thanks
     
  14. Bernard

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    I have abandond ckt on pg 4 in deference to pg 11, which I believe suits you'r need. 'never saw a repitition rate.
     
  15. darryl

    Thread Starter Member

    May 1, 2009
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    Thanks a lot blokes, for your help.
     
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